Recently, nonvolatile semiconductor memory devices represented by flash memories are prevalently used as data memory element of various electronic devices. As one of the important characteristics required of the nonvolatile semiconductor memory devices is the data retention characteristics. To improve the data retention characteristics, it is important that the constitutions of the devices are improved, and also the disturb stress in operations is mitigated to suppress the breakage of the stored data.
The followings are examples of related: Japanese Patent No. 3962769; Japanese Patent No. 4113559; Japanese Patent No. 4522879; Japanese Laid-open Patent Publication No. 11-003595; Japanese Laid-open Patent Publication No. 11-177069; Japanese Laid-open Patent Publication No. 2001-210808; Japanese Laid-open Patent Publication No. 2005-328023; Japanese Laid-open Patent Publication No. 2005-510889; Japanese Laid-open Patent Publication No. 2007-073894; Japanese Laid-open Patent Publication No. 2009-147304; Japanese Laid-open Patent Publication No. 2009-212292; and Japanese Laid-open Patent Publication No. 2011-171582.
Thus, the semiconductor memory devices of higher performance, which have the reliability improved by mitigating the disturb stress in operations are required.